1. Field of the Invention
The disclosed technology generally relates to methods of characterizing semiconductor materials, and more particularly to methods of characterizing shallow semiconductor junctions.
2. Description of the Related Technology
Shallow junctions are used to form various semiconductor devices, including transistors, diodes, isolation regions and active regions, to name a few. Parameters that can be measured to characterize the shallow junctions include concentration of active dopants and electron and hole mobilities, among other parameters. While such parameters can be measured after fabrication of the semiconductor devices, it can be advantageous to measure them in-line, i.e., during fabrication, of the semiconductor devices. Advantages of measuring the parameters in-line can include early detection of manufacturing discrepancies and obtaining information related to thermal evolution of the shallow junctions, among others. In addition, when measured in-line, it can be advantageous to measure the parameters without making physical contact to the devices to avoid contamination.
For the fabrication of shallow junctions for use in semiconductor devices such as for instance transistors, the activation anneal, which is typically applied after dopant implantation in a substrate, has often severe thermal budget limitations. As a consequence typically not all implanted dopants are activated.
For process development of shallow junctions or passivation layers it is important and/or advantageous to know electrical characteristics of the junction.
A straightforward method known in the art is the use of the so-called “four point probe” that measures the sheet resistance (Rs) of the upper junction layer, possibly in combination with secondary ion mass spectroscopy (SIMS), which then allows to determine the active concentration and dose. However the use of the “four point probe” method and SIMS relies on theoretical mobility values of the free carriers in the upper layer of interest. As the sheet resistance depends on the active dose and the average mobility of the free charge carriers in the layer of interest, the upper layer, measuring this mobility is important. This can be done by Hall measurements, but these are not straight forward and require special attention when contacting the sample. It is not an in-line metrology method and no mapping capabilities are possible.
Techniques for efficient in-line metrology that can directly measure the active dose and average mobility of the free charge carriers in a shallow junction are be limited.
Thus, there is a need for an in-line metrology method for measuring parameters associated with shallow semiconductor junctions.